The present invention pertains to a system for eliminating detonation or knock in an internal combustion engine and, more particularly, to a detonation control system for a two cycle engine utilizing microprocessor control for fuel injection and spark ignition timing.
Microprocessor-based engine control is well known in the automotive industry. Microprocessor control lends itself extremely well to the control of fuel injection and spark ignition in modern four-cycle automotive engines. Similarly, microprocessor engine control strategies may be applied to control fuel injection and spark ignition in two-cycle engines, particularly larger engines commonly used in marine applications. However, as is well known in the art, the construction and operation of a two-cycle engine varies greatly from that of a four-cycle automotive engine and, therefore, microprocessor control program strategies likewise vary considerably.
Thus, a two-cycle engine requires substantially different spark timing and fuel ignition strategies than a four-cycle engine. Also, variations in air and engine temperatures and in engine speed and other operating parameters require substantially different ignition and fuel strategies in a two-cycle engine as compared to a four-cycle engine.
The phenomenon of detonation, also referred to as engine knock, is common to both four-cycle and two-cycle engines. The prevention of detonation is primarily a function of engine design and construction, however, detonation may still occur in a properly designed engine. Detonation or engine knock is caused by premature self-ignition of the air fuel mixture which creates a pressure wave that interferes with the pressure wave caused by subsequent spark ignition of the fuel. Pre-ignition and knocking is often traceable directly to high engine temperatures. Detonation may become so severe or extend over a long enough period of time as to cause damage to the engine components.
It is known that improperly advanced spark timing may cause or aggravate detonation and that fuel mixture which is too lean may also promote detonation in an engine which is running somewhat too hot or is otherwise susceptible to occurrence of detonation. Thus, it is known that adjustments in the spark timing and in the fuel/air ratio can be used to correct a detonation condition.
U.S. Pat. No. 4,243,009 discloses a system for reducing engine knock in a two-cycle engine by enriching the air/fuel mixture. U.S. Pat. No. 4,667,637 describes a system for reducing engine knock by adjusting spark timing and/or enriching the fuel mixture. U.S. Pat. No. 4,777,913 describes an auxiliary fuel system operable to increase the fuel supply and reduce detonation. A detonation or knock detection circuit is disclosed in U.S. Pat. No. 4,761,992.
The use of microprocessor-based control of two-cycle engine functions, such as spark ignition and fuel injection, has made it desirable to utilize prior art analog strategies to enhance engine performance. The control of detonation is one aspect of engine performance that is amenable to microprocessor control strategy. The prior art analog detonation control systems typically provide increases in fuel enrichment and/or spark timing retard which are directly proportional to the magnitude of the engine knock. It has been found, however, that it is often desirable to provide non-linear incremental increases in the control parameters and/or to be able to vary the value of those increases, depending upon variations in certain operating conditions or on the type of engine in which the control is implemented.